Warragamba Dam

The Warragamba River flows through a gorge that varies in width from 300 to 600 metres (980 to 1,970 ft), and is 100 metres (330 ft) in depth. This gorge opens at its upper end into a large valley, the Burragorang Valley. This river configuration allows for a relatively short but high dam wall, in the gorge, to impound a vast quantity of water.[6]

In 1845, Paweł Strzelecki drew attention to the Warragamba River as a water supply catchment; in 1867, supporters proposed a dam. Between 1867 and 1946, supporters proposed various schemes before the site and design of the current dam received approval. In 1940, a weir and pumping station, known as the Warragamba Emergency Scheme, reached completion, just downstream of the main dam site.[6]

In 1943 the Metropolitan Water, Sewerage and Drainage Board invited the geologist William Browne to investigate a proposed site. Browne found a more suitable site and continued as geological adviser until completion.[7] The site was reviewed and approved by Dr John Savage, considered the pre-eminent expert in this field, and formally accepted by the Metropolitan Water, Sewerage and Drainage Board on 2 October 1946.[6] The Board appointed Thomas Upton as the engineer.

Dam construction began in 1948 and was completed in 1960. The resulting dam of the Warragamba River formed Lake Burragorang, which is one of the largest reservoirs for urban water supply in the world.

The dam wall comprises 1,612,000 cubic yards (1,232,000 m³) of concrete. It was laid as interlocking blocks roughly 17 metres (56 ft) on each side, which were later grouted together to form a continuous, monolithic wall. It is so large that engineers had to use two techniques to prevent the temperature from becoming too hot as the concrete set. One was to add ice to the wet concrete, the first application of this technique in Australia. The other was to embed cooling pipes into the concrete and circulate chilled water through the pipes. As a result, the dam wall was cooled in a few months instead of the estimated 100 years it would have taken to cool naturally.[6]

Spillway

Warragamba Dam

The main spillway has five crest gates: A central drum gate with a 27 metres (89 ft) clear span with a pair of radial gates on each side. Each radial gate has a 12 metres (39 ft) clear span. The drum gate is hinged along the upstream edge to the upstream crest and lowers into the dam wall to allow water to flow over it. When fully open, it forms a continuation of the crest profile.[6] All gates open automatically as the dam passes full water level, or can be manually opened.[6][8] The auxiliary spillway is normally closed by a series of fuse plugs that are designed to be washed away in the event of an extreme flood event.[2]

As originally designed, the dam could safely withstand a peak inflow of 500,000 cubic feet per second (14,000 m³/s), leading to a peak discharge of 354,000 cubic feet per second (10,000 m³/s) down the spillway.[6] Following a 1987 and 1989 re-evaluation of the potential rainfall and flood risks, the New South Wales Government authorised for the dam wall to be raised by 5 metres (16 ft) and constructed an auxiliary spillway on the east bank of the dam.[8]

One of the first places in the Gundungurra traditional homelands that most appealed to the Anglo-Celtic settlers were the river flats of the Burragorang Valley (now flooded under Warragamba Dam). Even before the valley was officially surveyed in 1827-8, many early settlers were already squatting on blocks that they planned to officially occupy following the issue of freehold title grants. From the Burragorang Valley and using Aboriginal pathways, other valleys to the west were occupied and developed by the settlers with construction of outstations and stock routes. These cattle entrepreneurs were then followed by cedar-wood extractors and miners.[3]

The Gundungurra traditional owners resisted the taking of their lands, and, relying on various laws of the colony at the time, continually applied for official ownership. Although their individual claims failed, in some kind of recognition of the significance of the designated tracts of land claimed, six Aboriginal Reserves (under the control of the NSW Aborigines Protection Board) were formally declared in the Burragorang Valley. Even after these reserves were revoked, many of the traditional owners remained, quietly refusing to leave their traditional homelands.[3]

Finally pushed into the "Gully", a fringe development in West Katoomba from about 1894, the Gully community stayed together for more than 60 years until dispossessed of the Gully by the then Blue Mountains Shire Council so a group of local businessmen could develop a speedway that became known as the Catalina Race Track. The Gully people kept talking about areas of land they had walked in as children - the nearby Megalong and Kanimbla Valleys and the Burragorang Valley. They knew of the profound significance of these valleys for their parents and grandparents.[9][3]

The construction site for the Warragamba Emergency Scheme was located on the east bank of the Warragamba River. Access to the site was along the road currently known as Weir Road. Major elements of the construction works still extant include the weir, a 10-cable cableway, shads, batching plants, roads, electrical substation, chlorination plant, maintenance staff accommodation, balance reservoir, Megarritys Bridge, water pumping station, tunnels, and associated pipelines.[3]

The catchment area is 9,050 square kilometres (3,490 sq mi). The areas closest to the lake, making up around 30% of the total catchment, are restricted access special areas. Most of the rest of the catchment consists of cleared farming land and contains large and small towns, which discharge treated sewage into the catchment.

Although the engineers did not design Warragamba Dam as a flood control measure, it can mitigate flooding by holding floodwaters back while the reservoir fills.

There is also a hydroelectric power station at the dam that can generate 50 megawatts (67,000 hp)[15] which is currently disconnected from the electricity grid.[16] Water levels became very rarely high enough, to allow operation of the power generators.

Warragamba Dam was also a popular picnic spot for Sydneysiders but access to the public had been restricted since 1999 due to A$240 million of upgrades in that time. It reopened to the public on 8 November 2009.[17]

Access to the dam wall and terrace gardens opened from 23 December 2012 to 28 January 2013 at weekends and public holidays.

The Emergency Scheme is representative of the collective engineering response to Sydney's critical water shortage during the Second World War period. It was the first stage in the storage and extraction of water from the Warragamba River, and was preliminary to the Waragamba Dam. All of the components are excellent examples of the civil engineering skills of the times; the Balance Reservoir is particularly significant because it provides a stilling pool downstream of Warragamba Dam for the purpose of flood discharge; the group of five cottages associated with the construction of the dam are considered to be of high significance because they housed the operations staff between 1940 and 1959. These have since been incorporated into the Warragamba township, one of the largest townships in the Shire of Wollondilly.[3]

The Warragamba Emergency Scheme was listed on the New South Wales State Heritage Register on 18 November 1999 having satisfied the following criteria.[3]

The place possesses uncommon, rare or endangered aspects of the cultural or natural history of New South Wales.

This item is assessed as historically rare statewide. This item is assessed as scientifically rare statewide.[3]

• 1998 Sydney water crisis
• Warragamba - township originally built to house dam builders.

Media related to Warragamba Dam at Wikimedia Commons

• WaterNSW - Warragamba Dam
• FloodSafe NSW Warragamba FAQ
• Sydney's Dam Levels - current statistics and graphs